Diglycerides have been found to be effective for improving blood cholesterol levels (WO 99/48378) and also to be effective for curtailing the accumulation of body fat and preventing adiposis (JP-A-04-300826, JP-A-10-176181). These effects are considered to be attributed to the inhibition of an increase in the level of fat in postcibal blood. Further, use of diglycerides in cooking oil is known to bring about such merits that upon frying, foaming is reduced and improved flavor and texture of the fried foods are assured (JP-A-02-190146, JP-A-07-016051, JP-09-154494). In addition, diglycerides are also known to be applicable to emulsified foods (JP-B-04-034367, U.S. Pat. No. 5,879,735, JP-A-03-008431). With the foregoing in mind, oil or fat compositions having a high diglyceride content have found wide spread utility as edible oils or fats for consumer use.
In the meantime, a technique has been disclosed in which an antioxidant and a crystallization inhibitor are added to diglycerides to improve their storage stability (JP-A-10-176181). Another method has also been disclosed, in which an organic acid is added before deodorization step to inhibit disproportionation reaction of the diglyceride to the monoglyceride and the triglyceride in a deodorization step of the oil or fat composition (JP-A-04-261497). Concerning food containers, on the other hand, a barrier resin technique (JP-A-51-112694) and a barrier coating technique (JP-A-2000-255579) for such containers have been disclosed to improve long-term storage stability of food.
As is appreciated from the foregoing, there is an increasing desire not only in Japan, but also in various countries in the world toward the use of diglycerides because of its superb health-promoting functions.
Depending on use conditions or storage conditions, however, the external appearances of oils or fats containing diglycerides may be impaired in some instances, because compared with triglycerides, diglycerides tend to become solid in cold temperature areas or tend to become turbid in high-humidity areas. Further, use of an oil or fat with moisture absorbed therein leads to stronger emission of an unpleasant smell upon cooking so that the flavor of cooked foods may be impaired in some instances.